This invention relates to particleboard, and more particularly to a novel foamed adhesive for use in the manufacture o particleboard.
The manufacture of particleboard heretofore has employed liquid or spray adhesive resins mixed with wood particles in a commercial blender. Because of the characteristics of commercial blenders, the resin is distributed over the wood particles quite inefficiently. Accordingly, the excessive amount of resin required to achieve adequate distribution over the wood particles for acceptable internal bond (IB) strength, modulus of rupture (MOR) and modulus of elasticity (MOE) reflects adversely on cost of production.
Investigation was made (Bonding Particleboard With Foaming Adhesives, by Alan Watters and J. D. Wellons, Forest Products Journal, Vol. 28, No. 2, February 1978) into the utilization of resin foam with the view to improve distribution over the surfaces of wood particles and thus achieve acceptable IB and MOR properties at lower production cost. This laboratory investigation utilized urea formaldehyde resin foamed with Freon 12 to 85 times the volume of the liquid resin, and concluded that the method employed in generating foams is not possible on an industrial scale.
Investigation into the use of foamed adhesives for particleboard also was made by Terry Sellers, Jr., and reported in his Technical Note entitled "Foamed Adhesives for Particleboard" published in Forest Products Journal, Vol. 38, No. 11/12, November/December 1988, pages 55 and 56.
This limited investigation utilized urea formaldehyde resin mixed with bodying agents and surfactants and foamed to four times the volume of the "neat" liquid resin that was used as a control and sprayed onto the furnish. The investigation found that IB and MOR properties were similar to liquid resin application at similar resin solids contents, and hence the resin costs were also about the same.
Thus, while resin foam has long been utilized successfully in the efficient production of plywood, as exemplified in U.S. Pat. Nos. 3,895,984; 3,905,931; 3,965,860; 4,115,178; and 4,258,088 such resin foams heretofore have not been employed in the commercial manufacture of particleboard.